This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-145227, filed May 17, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus which can be fitted with an offset stacker that allows image-formed sheets of paper to be offset stacked in the discharge tray, a copying machine equipped with the image forming apparatus, and a method of controlling the image forming apparatus.
2. Description of the Background Art
The offset stacker is one of the stacking devices that can be fitted to the paper discharge section of an image forming apparatus. The offset stacker allows finished sheets to be offset stacked in the discharge tray for automatic sorting thereof. Thus, the sheets cannot be sorted normally unless a predetermined relationship is maintained between the discharge timing and the offset timing.
However, the discharge timing and the offset timing can be displaced relative to each other due to failures or malfunctions. In that event, the sheets are discharged to wrong positions on the discharge tray and the user may suppose that the sheets are being sorted correctly without noticing wrong discharge to the discharge tray.
To date, various types of offset stackers have been developed. Among them is one that has offset discharge rollers. This type of offset stacker is equipped with a mechanism for moving the discharge rollers adapted to discharge finished copies to the discharge tray in a direction perpendicular -to the direction of paper transportation. By moving the discharge rollers with the paper pinched, the places where copies fall into the discharge tray are offset.
With such an offset stacker, the displacement of the discharge timing and the offset timing may disturb the paper transportation, resulting in a paper jam.
At the occurrence of a paper jam, the user has to remove the jammed paper, which imposes an extra burden on the user and may also damage the machine.
Where the image forming apparatus is of an electrophotographic type, the operation of the thermal fixing equipment has to be stopped in the event of a paper jam, which requires an appreciable amount of time to restart the image forming operation after removal of the jammed paper.
It is an object of the present invention to prevent improper paper discharge when a malfunction occurs in the offset stacker.
The object is attained by an image forming apparatus which forms an image on a predetermined paper form transported by a paper transport mechanism on a predetermined paper path using image forming means and can be fitted with an offset stacker which, in discharging paper forms after being formed with images into a discharge tray, offset stacking the image-formed paper forms in the discharge tray, comprising error detection means for detecting an error in the timing of offset stacking by the offset stacker; and forced stopping means responsive to the error detection means for forcing the paper transport mechanism and the image forming means to stop their operation when an error is detected by the error detection means.
Moreover, the object is attained by a copying machine which includes an image scanner for scanning an image on each of the originals and an image forming apparatus for forming an image scan by the image scanner on a paper form transported by paper transport means on a predetermined paper path using image forming means and can be fitted with an offset stacker which, in discharging paper forms after being formed with images into a discharge tray, offset stacking the image-formed paper forms in the discharge tray, comprising error detection means for detecting an error in the timing of offset stacking by the offset stacker; and forced stopping means responsive to the error detection means for forcing the paper transport means and the image forming means to stop their operation when an error is detected by the error detection means.
Furthermore, the object is attained by a method of controlling an image forming apparatus which forms an image on a predetermined paper form transported by a paper transport mechanism on a predetermined paper path using image forming means and can be fitted with an offset stacker which, in discharging paper forms after being formed with images into a discharge tray, offset stacking the image-formed paper forms in the discharge tray, comprising the steps of detecting an error in the timing of offset stacking by the offset stacker; and forcing the paper transport mechanism and the image forming means to stop their operation when an error in the timing of offset stacking is detected.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.